FTIR STUDY OF THERMAL-OXIDATION OF ENR

Thermal oxidation of two grades of purified epoxidized natural rubber (ENR 25 and ENR 50) and one grade of unmodified natural rubber (purified SMR L grade) were studied using Fourier Transform Infrared Spectroscopy (FTIR). Changes in the characteristic absorption band, particularly the hydroxyl and carbonyl peaks of the degraded rubbers are carefully monitored. Results indicate that thermal oxidation occurs in the double bond region for SMR L to form oxidative products which mainly consist of hydroperoxide, hydroxyl and carbonyl compounds. In the case of ENR, thermal oxidation occurs not only in the double bond region, but also involves epoxide ring-opening reaction to yield oxidative products having similar functional groups as that of SMR L. For the three rubbers studied, increasing temperature of thermal oxidation increases the rate of oxidation. From a time-dependent study, it suggests that thermal oxidation of ENR is an autocatalytic process. No attempt, however, is made to ascertain the exact chemical structures of the oxidative products formed in this study.